1. Field of the Invention
The present invention relates to a lens shutter device, more particularly to a lens shutter device by which a high speed shutter operation is easily obtained.
2. Description of the Related Art
To meet the needs for miniaturization, high effectiveness, and lower costs, of a camera, conventionally lens shutter devices having various constructions or qualities, such as precise control achieved by using a stepping motor, reduction of costs by using a bimorph cell, and an automatic focusing and automatic exposure control by a single motor, have been proposed. With a lens shutter device having a stepping motor as a drive source, however, it is difficult to obtain a high torque and a high speed shutter operation, and if a bimorph cell is used as a drive source, due to the influence of a magnetic hysteresis, it is difficult to obtain an exact proportional relationship between the voltage and the displacement, and therefore, a precise control cannot be achieved. In a lens shutter device having an ordinary core motor as a drive source, a construction by which shutter sectors are open and closed by a rotation of the motor and by a spring force, is often adopted. However, since an ordinary motor rotates at a high speed and can not be accelerated with precise control, it is difficult to obtain a high speed shutter operation, and therefore, the high speed shutter operation is limited to about 1/500 sec. In particular, due to the lengthening of the focal length of lens and the increased diameter of the open aperture, the time required for the shutter to be fully opened, has become longer, which restricts the limits within which camera vibration can be ignored, and lowers the photographing range.